1. Field of the Invention
Variable capacity wobble plate type compressors having means for changing the angle of the wobble plate to control the stroke length of the compressor.
2. Description of the Prior Art
U.S. Pat. No. 3,861,829 (Roberts et al), assigned to the same assignee as the present invention, describes a wobble plate compressor using controlled, under-piston gas pressure to vary the inclination of the wobble plate, which is supported on a universal joint. The present invention is an improvement on Roberts et al in that a fluid actuator is employed to move the wobble plate.
U.S. Pat. No. 3,552,886 (Olsen) shows a spherical bearing or hinge ball supporting the drive plate/wobble assembly to a point spaced from the drive axis to maintain essentially constant clearance volume.
U.S. Pat. No. 3,062,020 (Heidorn) discloses an automotive air conditioning compressor of the same general type as the present invention, except it contains an oil pump and relies on oil pressure to produce a stroke decreasing force on the wobble plate. During long periods of unloaded operation, the oil has a tendency to leave the compressor and excessive loss of oil causes the compresor to go into stroke until sufficient oil is returned to the compressor. Also, there are certain transient conditions when the refrigerant boils out of solution with the oil and foaming in the inlet to the pump causes loss of oil pressure. Both of these conditions may cause the compressor to operate for extended periods when air conditioning is not desired. The present invention relies on a very small minimum stroke which maintains a small pressure differential across the compressor. The discharge pressure is used to hold the wobble plate in minimum stroke.
U.S. Pat. No. 2,711,135 is directed to a pump with the zero stroke condition at bottom dead center and consequently is unsuitable for a compressor. Also, this design takes the torque reaction of the wobble plate through the pistons with a wrist pin arrangement instead of a ball joint. This will cause severe edge loading, and rapid wear of the pistons and cylinder bores.
U.S. Pat. No. 2,942,551 (Thompson) shows a fuel injection system where the rim of the wobble plate bears against the ends of bellows instead of having pistons and rods. There is no necessity to anchor the outer rim against rotation in this system. Also, the stroke changing mechanism is by mechanical linkage actuated through a control rod (presumably to the accelerator pedal or some intermediate control). The mechanical design is completely different from the present invention.
U.S. Pat. No. 2,344,517 (Schnell) describes a hydraulic pump having a roller on the driving member which forces the wobble plate element to nutate. A centrally located control piston activated by discharge pressure forces the wobble plate toward the maximum stroke. A variable maximum stroke stop is controlled by centrifugal weights so that the maximum stroke reduces with increasing speed.
U.S. Pat. No. 3,575,534 (Leduc) concerns a hydraulic pump with a pivot location which maintains a more nearly constant top dead center position than centrally pivoted units, and has a centrally located control piston powered by discharge pressure to reduce the stroke. The control is designed to reduce the stroke with increasing pressure such that a constant input torque is maintained. Relatively small diameter pistons and slippers are used. The mechanical design is quite different from the present invention.
Copending applications: Abendschein et al, Ser. No. 655,799 and Close et al, Ser. No. 655,797, filed Feb. 6, 1976, disclose improvements on the Roberts et al '829 compressor; but in each of the foregoing, the pressure in the crankcase is utilized to control the position of the wobble plate by the net forces on the pistons and the leverage attributable to the pivot point being spaced from the drive shaft axis.